The prior art contains numerous examples for detecting a filament or strand as it is being advanced. Many of these prior art devices use a light source and reflected light from the strand to actuate a light sensor and provide a strand presence signal.
One such prior art device is U.S. Pat. No. 4,010,908 which shows a guide for a filament or stand, and a fiber optic system for supplying light to the guide and for receiving light reflected from the strand. Other examples of using reflected light to sense the presence of the strand are shown in U.K. Pat. Nos. 1,124,590, and 779,548 in addition to the prior art cited in U.S. Pat. No. 4,010,908.
However, these prior art patents must flood the filament detection area with light or must force the filament into the detection area either subjecting the system to a low signal to noise ratio in the one case or the filament itself to abrasion in the other case. In addition, these prior art devices require a more powerful light source than the solid state light source used in the invention.